Rotary ball valves are used in a wide number of process control system applications to control some parameters of a process fluid such as a liquid, gas, slurry, etc. While the process control system may use a control valve to ultimately control the pressure, level, pH, or other desired parameter of a fluid, the control valve basically controls the rate of fluid flow.
Typically, a rotary ball valve includes a valve body defining a fluid inlet and a fluid outlet. A ball element is mounted in the valve body and rotates about an axis into and out of abutment with a seal assembly, thereby controlling the amount of fluid flow through the valve.
Rotary ball valve components, including the valve body, the ball element, and the seal assembly, are typically constructed of metal. This stands especially true when used in high pressure and/or high temperature applications. However, the ball element and seal assembly can suffer wear due to the continuous engagement of the ball element and seal assembly during opening and closing of the valve. The problems resulting from the wear include, but are not limited to, diminished life span of the valve components, increased frictional forces between the ball element and the seal assembly, and undesirable leakage between the ball element and the seal assembly, as well as between the seal assembly and the valve body. Similarly, because the frictional forces tend to increase as the components become more worn, the dynamic performance and control characteristics within the valve are worsened, resulting in inefficiencies and inaccuracies in the valve. To alleviate some of these concerns, some seal assemblies are biased such as to provide a more reliable seal against the ball in the closed position.